On the contrary, the EPZ-6438 reduction of plasma volume buy GSK2879552 in R1 reflected in body mass reduction might be caused by dehydration, although the decreased plasma volume could be shown as a hemoconcentration due to the acute effect of strenuous endurance on hematological parameters [23]. The activation of the RAAS (renin-angiotensin-aldosterone-system) could lead to an enhanced

retention of Na+ and free water, resulting in an increase in plasma volume and a decrease in plasma [Na+] [2, 58]. Presumably, the increase in plasma volume in R2-R4 and the retention of water was due to an increased activity of both vasopressin and aldosterone [1, 2, 12, 16, 19, 57, 59]. Urinary indices are suggested as parameters of hydration status [53, 60, 61], however several studies have documented that they are not accurate measures of hydration status immediately following exercise activity [62] and plasma osmolality would be a better marker of hydration status in the situation of acute dehydration [58, 63]. Plasma osmolality remained stable in all races with a non-significant increase despite a decrease in plasma [K+] in R3 and a decrease in plasma [Na+] in R4. An increase in transtubular potassium gradient could be responsible Salubrinal order for a preservation of both plasma [Na+] and body water during ultra-endurance exercise due to an increased activity of aldosterone [8]. We

assume that this may explain why plasma osmolality was stable in all races despite a loss in body mass. These findings support recent findings in Tam et al. [63] that the body primarily defends plasma [Na+] and aids at maintaining [Na+] and osmolality in plasma, but not body mass during endurance performance. In ultra-marathoners, plasma [Na+] and plasma osmolality are well

regulated and do not change while drinking ad libitum[58]. Changes in urine [Na+], urine [K+], urine specific gravity and urine osmolality in normonatremic finishers (n = 50) Since GPX6 hematological parameters such as plasma [Na+] or hematocrit were not valid indicators for the detection of mild hypohydration [61], urine parameters such as colour, urine specific gravity, and urine osmolality were considered to be valid indices of hydration status [61]. The decrease in body mass might be due to dehydration since urine specific gravity as a sign of dehydration [60, 61] significantly increased in all cycling races (R1,R2,R4), and non-significantly increased in R3. Cyclists (R1,R2,R4) lost approximately 2.3% of body mass, with urine specific gravity of > 1.020 mg/l indicating dehydration [64], ultra-runners (R3) were minimally dehydrated according to changes in urine specific gravity. On the contrary, the use of urine specific gravity as a marker of hydration status is time-dependent and shows only chronic dehydration, but not acute dehydration [53].